Plastic packages such as cases for CDs or DVD disks have been manufactured for several years. To the best of my knowledge, the commercial versions are manufactured by injection molding. The typical case comprises a center hub for receiving the disk hole on which can be mounted the disk by pressing the disk onto the hub. The so-called "jewel case" for CDs comprises a hub with radial slits which move radially inward under the disk pressure until the disk seats on the hub. The disk can be removed by lifting the disk outer edge until the disk lifts off of the hub. This construction is, however, considered unsatisfactory for DVD disks that contain much more information than the CD, and thus DVD suppliers require cases that use a push-button scheme to unmount the disk. In the cases currently available, again they are constructed by injection molding because of the need for accurate control of the dimensions of the center hub and the disk release mechanism.
One of my earlier U.S. Pat. No. 5,353,932 (the '932 patent), whose contents are herein incorporated by reference, describes and claims a process for making video cases for cassette tapes using vacuum forming techniques. A typical vacuum forming process consists of thermoforming a relatively rigid thermoplastic sheet, such as polyvinyl chloride (PVC), to form opposed inner contoured surfaces configured to receive and hold the video cassette or other object when the case is closed by folding about its spine, then covering the back side of the rigid sheet with, in turn, a cardboard stiffener, an opaque relatively flexible PVC sheet, and a clear relatively flexible PVC sheet, followed by heat-sealing together the sandwich so formed so as to seal the cardboard stiffener between the rigid PVC and the flexible opaque PVC sheets and the latter to each other and to the clear PVC sheet around three sides so that advertising material for the contents of the case can be inserted through the unsealed fourth side and thus be visible to prospective customers and users of the video cassette. Typically, for PVC, the relatively rigid sheet has a thickness between about 0.012 and 0.030 inches (in.), and the relatively flexible sheets have thicknesses ranging between about 0.003 and 0.020 in. The term "rigid" or "relatively rigid" is a term of art meaning a sheet thickness that will hold its shape when thermoformed, that is usually but not always thicker than the flexible sheet or relatively flexible sheets, but that still has sufficient flexibility to allow the case to bend easily around its spine and thus easily open and close. However, this degree of flexibility is insufficient to stiffen the case sides, which in use are not supposed to bend. Hence, it is common practice to insert a stiffener member in the case sides to stiffen the latter. Typically, the stiffener member is made of a non-heat-sealable material such as, for example, inexpensive cardboard about 0.018 to 0.120 in. thick, with score lines or slits defining a center spine to allow the flat sides of the stiffener member to bend around the score lines or slits when the case is closed.
It is desired to use the vacuum-forming scheme described in the '932 patent to manufacture a case for a DVD disk which utilizes a push-button scheme to unmount the disk. While most of the relevant prior art I am aware of uses injection molding schemes, I am also aware of two patents that do describe the use of vacuum forming for the manufacture of a CD or DVD disk. The first, U.S. Pat. No. 4,819,799, describes a central hub surrounded by a ledge on which the disk sits. Depressing the hub releases the disk. Few details on the construction of the hub which allows it to perform its functions are given in this patent, as the patent is mostly concerned with the sealing of the disk package from both sides. The second, Japanese Patent Disclosure No. 2-205589, published Aug. 15, 1990, discloses a center button surrounded by four spaced peripheral sections in turn surrounded by a ledge for supporting the disk when mounted. Each of the four peripheral sections have detent edges that hold the mounted disc, and which, when the center button is depressed, cause the detents to move inwardly allowing the disk to be removed. This Japanese document prefers to include a separate spring cushion between the ledge and a bottom plate which is sealed to the upper part to ensure an adequate restoring force when the center button is depressed. This construction with two sealed elements defining the case center and with the presence of the separate spring cushion undesirably increases the cost of manufacture. As described in the '932 patent, so-called turntable machines are employed in the sandwich assembly process, during which at stations situated around the turntable the case elements, including the thermoformed rigid member, the stiffener member, and the two flexible sheets, are assembled and at a final station the assembled sandwiched elements are heat-sealed together in a single step to complete the assembly. The case described in the Japanese document does not lend itself to manufacture by this process at acceptably high production rates.